The present embodiments relate to planning in nuclear medicine, such as positron emission tomography (PET). In particular, planning is provided for detecting from a volume of the patient that is longer than the field of view of the PET detector.
PET user interfaces support examination planning based on multiple integral bed positions. In this “stop and shoot” approach, different bed positions are dictated by the physical axial length of the PET detector. For example, the examination is divided into a plurality of bed positions spaced less than a length of the PET detector apart. The examination region for each bed position corresponds to the length or field of view of the PET detector. These bed positions are arranged to provide overlapping examination at different locations.
To define the region to scan of the patient, the user indicates the starting bed position. The amount of overlap may be defined as well. Since each bed position has a length based on the PET detector, the user defines the number of bed positions and overlaps to provide for examining a diagnostic region of interest of the patient. The user configures only the number of integral bed positions to define the overall extent of scan. The user can determine the location of one end of the overall scan range, but the other end location and the positions of the individual bed positions are determined based on the integral math of gantry axial field-of-view. The integral math may not match the anatomy of the patient with specific bed positions. The user cannot easily optimize and adapt the examination protocol to the specific needs of various organ imaging. As a consequence, most users do not attempt to optimize scanning protocols for the different bed positions.
Another problem with typical PET examinations is sensitivity. The sensitivity profile of the PET detector across the axial field of view is triangular or trapezoid shaped, which leads to lower sensitivity and lower signal-to-noise ratio at the end planes of a given bed position. Where multiple bed positions are used, the overall sensitivity profile is generally more consistent within the diagnostic region of interest, but has decreased sensitivity and signal-to-noise ratio at the extremes due to no overlapping bed positions. Users compensate for the lowered sensitivity and signal-to-noise ratio by manually planning to begin and end the examination in positions that are beyond the area of diagnostic interest. This further complicates planning for the bed positions and results in imaging of parts of the patient that are not diagnostically desired. Alternatively, the users accept the lowered sensitivity and signal-to-noise ratio at the end planes.
During operation of the PET detector after planning, the user and patient are presented with progress references in the form of beds “X” of “Y” and/or time remaining per bed or for the overall scan. The user or system may provide a general instruction to the patient prior to the beginning of the overall scan, or the user may attempt to manually provide the instruction based on the coarse progress information. Since general instructions have minimal benefit as not timely and improper timing may lead to a reduction in examination quality, the user typically chooses not to give patient instructions during the examination itself and does not attempt advanced techniques, such as breath-hold during whole body examinations.